Here is a tip that works for me. Maybe you already know it?
Anyway, I open the hood, take an electric hair dryer and point it into the air cleaner intake and turn it on. My 300 TDT starts up in really cold weather, even without my block heater plugged in, when I blow the hot air in the intake.
On my 300 D there is a plastic flex hose that comes off on one end really easy and my hair dryer fits nice into that.
Paul Fretheim